We are requesting partial funding for the fourth conference in The Cooper Institute Conference Series entitled, "Innovative Approaches to Understanding and Influencing Physical Activity." This is a timely topic because the field of behavior change in general and physical activity in particular has come to recognize that the behavior of individuals occurs within a context of situational, social, and environmental influences. The proposed conference will bring together experts from diverse fields in an effort to further existing dialogue concerning the factors that mediate physical activity behavior. Potential mediators include the psychological, affective, behavioral, interpersonal, sociocultural, ecological, transportation, environmental, and policy factors that are believed to influence physical activity behavior. The conference is important because physical inactivity represents one of the leading public health burdens currently facing our nation. Abundant scientific evidence demonstrates that physical inactivity is associated with increased morbidity and mortality, and it is estimated that 250,000 deaths per year are attributable to a lack of regular physical activity. The objectives of the conference are to: (1) assemble a diverse group of experts to summarize what we know about factors that influence physical activity behavior; (2) stimulate analyses of existing data from physical activity interventions and transportation and urban planning; (3) discuss measurement and analysis of physical activity behavior to improve the measures and methodologies employed to statistically model the effects; and (4) disseminate these findings to professionals in all fields with potential to influence physical activity behavior. The scientific program committee is unaware of any other international, national, regional, or local meeting that has focused exclusively on these objectives. Also, we do know that these topics are of great interest to other groups from which we are also soliciting funding, including the Centers for Disease Control and Prevention and the Robert Wood Johnson Foundation. Based on our previous record of successful organization and execution of conferences resulting in far-reaching publications, we are confident that we can build on this success to develop, organize, and publish conference findings that will be influential in promoting physical activity programs to increase the prevalence of activity in sedentary populations.